1. Field of the Invention
The present invention relates to the structure of a PTO portion of a tractor.
2. Description of the Related Art
Conventionally, as one mode of a tractor, there has been known a tractor in which a PTO clutch is mounted in the inside of a rear housing and, at the same time, the PTO clutch adopts a friction multi-disk-type hydraulically operated clutch structure (for example, see patent document 1 (JP-UM-B-7-51393).
Here, the PTO clutch is communicably connected with a hydraulic pump by way of a clutch changeover valve. The clutch changeover valve is allowed to perform the changeover operation using a manipulation jig and can take a half-clutch state.
By supplying working oil to the PTO clutch so as to bring the PTO clutch into the connection state in this manner, it is possible to transmit the power to a PTO shaft. In this case, the clutch changeover valve is temporarily brought into the half clutch state by way of the clutch changeover valve using the manipulation jig and, thereafter, the PTO clutch is brought into a complete clutch connection state so as to prevent the power from being rapidly transmitted to the PTO shaft.
Further, as one mode of a tractor, there has been known a tractor in which while an engine is arranged in a prime mover portion, an inner-and-outer duplicate shaft structure is arranged in the clutch portion, wherein the inner-and-outer duplicate shaft structure is constituted of an inner drive shaft which extends in the longitudinal direction and a cylindrical outer drive shaft which surrounds an outer periphery of the inner drive shaft. The inner drive shaft is interlockingly connected with the above-mentioned engine by way of a PTO clutch, while the outer drive shaft is interlockingly connected with the engine by way of a traveling clutch thus providing the dual clutch structure which includes the PTO clutch and the traveling clutch (for example, see patent document 2 (JP-A-8-80754)).
Further, a clutch pedal is mechanically and interlockingly connected with the PTO clutch by way of a rod or the like, wherein it is possible to perform the connection and disconnection operation of the PTO clutch by performing the step-in manipulation of the clutch pedal.
Here, the above-mentioned inner drive shaft is interlockingly connected with the PTO portion by way of a PTO-system power transmission mechanism arranged in the inside of a transmission portion. Further, the above-mentioned outer drive shaft is interlockingly connected with a pair of left and right rear wheels by way of a traveling-system power transmission mechanism arranged in the inside of the transmission portion.
However, the tractor disclosed in the above-mentioned patent literature 1 has following drawbacks.
(1) Since the PTO clutch is incorporated in the inside of a rear housing, it is difficult to separately provide a specification which includes the PTO clutch and a specification which has no PTO clutch while using the rear housing in common.
(2) The structure which temporarily brings the PTO clutch into the half clutch state by way of the clutch changeover valve using the manipulation jig and, thereafter, brings the PTO clutch into the complete clutch connection state is complicated and pushes up a manufacturing cost.
On the other hand, the tractor disclosed in the above-mentioned patent literature 2 has following drawbacks.
(1) Since the PTO clutch is arranged in the inside of the clutch portion, it is difficult to mount and dismount the PTO clutch. As a result, it is difficult to separately provide a specification which includes the PTO clutch and a specification which has no PTO clutch while using the clutch housing in common.
(2) The inner drive shaft which is interlockingly connected with the PTO portion by way of the PTO-system power transmission mechanism and the outer drive shaft which is interlockingly connected with the pair of left and right rear wheels by way of the traveling-system power transmission mechanism are formed into the inner-and-outer duplicate shaft structure and are arranged in the inside of the transmission portion and hence, there arises a drawback that the structure in the inside of the transmission portion becomes complicated and large-sized thus pushing up a manufacturing cost.
(3) The inner drive shaft is interlockingly connected with the engine by way of the PTO clutch and, at the same time, the outer drive shaft which is interlockingly connected with the engine by way of the traveling clutch thus forming the dual clutch structure which includes the PTO clutch and the traveling clutch and such dual clutch is arranged in the clutch portion and hence, there arises a drawback that the clutch portion becomes complicated and large-sized thus pushing up a manufacturing cost.